Inflatable bladders are sometimes used as mandrels to produce fiber reinforced resin parts. Multiple plies of fiber reinforced resin are laid up over the mandrel in order to form the plies into the desired part shape. The mandrel may be removed from the layup after the layup is compacted or cured by collapsing the mandrel to reduce its cross sectional shape so that it can be withdrawn from the part.
In some applications, the ability of the bladder to apply pressure uniformly over the layup may be dependent on the bladder's dimensional stability. Maintaining dimensional stability of the bladder may be particularly problematic in the case of long tubular composite part layups.
One type of known mandrel used for layup and curing of composite parts employs a reinforced silicon rubber bladder, however this type of bladder demonstrates relatively rapid, continuous shrinking over time with repeated use and therefore may not provide uniform pressure during cure cycles. In the case of parts having relatively strict dimensional requirements, reinforced silicon rubber bladders may be used only once because of their inherent problems with thermal growth and post-cure shrinkage.
Another type of mandrel uses nylon tubular bagging film to provide autoclave pressure during curing to the internal cavity of a part. However, bagging film does not have the required structural strength and rigidity to support a part during the layup process.
Accordingly, there is a need for a collapsible mandrel exhibiting improved dimensional stability over repeated uses, and which possesses the necessary strength and rigidity to allow the mandrel to be used for part layup.